Research On Secure And Efficient Spectrum Handoff Algorithm In Cognitive Radio Networks

In order to solve the problem of shortage of spectrum resources and low spectrum utilization,cognitive radio technology came into being.Cognitive radio technology allows unlicensed users to opportunistically use the idle licensed spectrum,but needs to be retired in time when the primary user appears.In order to ensure the continuity of the communication,the secondary user will have a spectrum handoff.In the spectrum handoff process of cognitive radio networks,secondary users are generally considered to be trusted.However,in the actual network environment,secondary users in the network may generate selfish behavior or malicious behavior for their own benefit.Selfish or malicious behavior of secondary users will result in a gradual decline in spectrum utilization efficiency and network performance(throughput,etc.).In order to enhance the security of spectrum handoff and improve the performance of secondary users,this thesis first establishes a reputation system in the cognitive radio network,and then analyzes the availability of the spectrum based on the establishment of the reputation system.The main work of the thesis is as follows:In the cognitive heterogeneous wireless network,the problem of network performance degradation caused by secondary users' selfish or malicious behavior in the spectrum handoff process,this thesis proposes a spectrum handoff mechanism based on the reputation system.Firstly,by extracting the user behavior characteristic information,the behavior of the secondary user after accessing the channel is evaluated,and the reputation value is determined according to the behavior of the secondary user,and the reputation system is established at the cognitive base station.Secondly,the secondary user is ranked according to the credit status of the secondary user,and the secondary user is assigned a channel of the authorized channel or the shared frequency band according to the hierarchical situation of the secondary user.In the process of accessing the licensed spectrum,when the user waits for the delay request,the secondary user with a high reputation value has a higher access priority.The simulation results show that the proposed method can effectively improve system throughput,reduce handover and outage probability,reduce the chances of low-reputation secondary users accessing licensed spectrum,and improve system security.In the cognitive heterogeneous wireless network,after the introduction of the reputation system,although the security of the system is enhanced,the handoff performance of the secondary users needs to be further improved.Therefore,this thesis proposes a spectrum handoff mechanism based on spectrum availability.First,the activity of the primary user is modeled by the Markov process,and the spectrum idle probability and estimated available duration are analyzed based on historical information.Then,the availability of the spectrum is considered separately according to the type of service of the secondary user.In the process of spectrum handoff,the secondary users are ranked according to the reputation and service type of the secondary users.Secondary users with high ratings have priority access to channels with better availability.The simulation results show that the proposed algorithm can effectively reduce the handoff probability and handoff delay,and improve the throughput of secondary users when the channel resources are limited.